BBS stands for "Bulletin Board System." It's a way to let people use your computer over the telephone. It lets them leave messages much like a paper-and-thumb-tack bulletin board does.
Traditional BBSs and this first version of HyperBBS communicate with users who dial up the system via a very simple, text-only interface. Users use a "terminal program" (such as Red Ryder, Microphone, or MacTerminal) to interact with the BBS.
Besides public messages, BBSs provide users with private mail and public domain or shareware files.